What Jason and Fixr said is spot on with what I learned in my psychology of sleep class a few years ago in college. I was that stereotypical teenager who stayed up all night and slept all day, was totally nocturnal, though I did exacerbate it by shifting my circadian rhythm enough that instead of just sleeping in and going to bed late, I would wake up at 4-5pm and go to bed like at 6am. My father was NOT happy about that. These days I can get to bed at 10pm and wake up at 7am.

As for Rachael's questions, from what I remember, part of it is individual. Some people get by on less sleep, some on more. I need about 9 hours whether i'm diurnal or nocturnal. If I get less, say 5-6hrs, I can only go a few days before i start needing naps to get by. If I get more, I wake up groggy. I have really intense sleep inertia though so it's really easy for me to go 10+ hours sleeping. It actually really sucks cos it can be a total waste of time, as much as I love sleeping.

That being said, we are naturally inclined as humans overall to diurnal, as William quoted above, because of our hormone regulation. This is why people can take certain chemicals to help lessen jet-lag. However, we DO have a circadian rhythm that can be, if memory serves correctly, gradually shifted around, which is why people can be either nocturnal or diurnal, depending on their current lifestyle (but as already mentioned, some people cope better than others).

So it really is a mix of both nature and nurture, as with most things. Pretty much everyone's circadian rhythms can be shifted to be nocturnal, but some people just naturally handle better with it than others, or even prefer it. Kind of like how for the most part, anyone can survive on any diet (barring allergies/intolerances/ etc.), but individuals tend just naturally do better with some diets than others.

edited to credit Fixr as well since he posted first about the teenage sleeping pattern thing.

I sleep from 6am till 2pm usually. I do adjust back to a day schedule a few times a year for variety and to adjust to doing conventions but it always slips back to later and later eventually but I have found that 8am is absolutely the latest (earliest?) I can go to bed without feeling off. I do find that getting up at 2pm still affords me plenty of time to do errands and be out among the muggles. Working at home makes it easier to adjust and I do better and more work if I do the late night shift. I assume this is due to a lack of contact from other people. The texts stop, emails stop rolling in, etc. Also, I despise heat and humidity with a passion and it is always more pleasant at night, everywhere, any time of the year.

Jason, you just mostly just restated everything that Fixr just wrote. I agree with your point though, highschool and elementary schools should definitely switch. Also, I wonder if not "shifting back" and maintaining nocturnal sleeping patters is a symptom of a larger issue, like the rate of brain maturity.

Maybe it's not a rate of brain maturity, but rather a hormonal imbalance? You've mentioned before that your body fixed itself up in certain regards once you started eating soy for the phyto-estrogens, maybe there's something going on with the sleep related hormones, too. Given how sensitive our bodies are to various hormonal imbalances (depression, acne, weight, etc.) I wouldn't be surprised at all if that were the cause to natural nocturnal tendencies. Hormonal imbalances aren't necessarily the brain's fault, in many causes it's other organs or glands that aren't quite doing their job.

I should go dig out the book we had to use for my sleep psychology class. It's more of a primer, not a full on text, but still has some useful info.

I've been thinking a bit about the health problems with night shift workers. I guess that most night workers would be natural day people, which makes me wonder if night workers who prefer being up at night suffer the same problems (weight gain, etc.) or if the average is just skewed by the day-walker majority.

Then there's the fact that most (all?) shift work is done in rotation. My sister works a security job and she does something like 4 days, 4 nights and then 4 days off. I know a nurse whose shifts rotate too. Surely that continual shifting of the circadian rhythms is going to be more harmful? Not sleeping enough seems to have the same health issues as working the night shift, so maybe the continual shifting results in worse sleep...

I don't suffer from weight gain but the mentioning of it does remind me that most of my coworkers tend towards heavier set folk. Not sure if it's from working in a kitchen, or the night shift, or both.

Well, a few years ago when I was even more strictly nocturnal, I'd visited a rheumatologist, and she told me my vitamin D levels were dangerously low. In addition, my white blood cell count was rather high (which is generally an indication for the body struggling to fight something off). After going on a prescription of Vitamin D for two months, my blood tests came back totally fine. So... it seems that without vitamin D, my body was not keeping itself going well. I'd listened to an episode of Quirks & Quarks that discussed vitamin D, and it proposed that D was the master key through which all other vitamins were absorbed. I take vitamin D these days, to counter my tendency towards nocturnalism.

This is the first place I could find anythin about this but let me tell you all nocturnality in humans is real but rare I was told by my g.p I have the form of genetic nocturnilaity wich cannot harm me or cause me any damage at al it just put a reverse state on me cardial systen wich make's me eat from 10.00pm after waking at 9.00pm an therefore allows me to gain the energy I would have through the day but throughout the night. If you have any thoughts onit please get in touch.